The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Embodiments of this invention relate to compositions and methods used in treating a well, a subterranean formation penetrated by the well, or the like. In particular, embodiments relate to the viscosity reduction of polymer gels after use in hydraulic fracturing, sand control, workover operations, and the like. In particular, embodiments provide peroxide means to reduce the viscosity by reducing the molecular weight of the polymer, whether or not the polymer is crosslinked.
Hydraulic fracturing is a process for stimulating oil and gas wells by pumping gel-proppant slurries at high pressure into producing rock layers. Once the rock is cracked, the resulting fracture is propped open by the sand or other proppant carried by the slurry. This fracture serves as a highly conductive path for the oil or gas, and therefore increases the effective well-bore radius. Fluid viscosity can facilitate effective proppant placement during fracturing operations. Polysaccharides such as guar and guar derivatives have served as common viscosifying polymers. They are often crosslinked using borates or metallic crosslinkers such as zirconium and titanium to generate even higher viscosity.
Once a particular subterranean formation treatment operation is essentially complete, it generally becomes necessary to break, i.e. substantially reduce, the viscosity of the fluid, such as a polymer gel, by reducing the molecular weight of the polymer network forming the gel. This industry uses a variety of compounds to break the viscosity of fluids, including those defined in the broad categories of oxidizers and enzymes. The break mechanisms involved are generally complex, and poorly understood, and therefore breakers are oftentimes not adequately effective or easily usable. Control over the timing of viscosity reduction is highly desirable in subterranean treatment operations. Factors such as pump time, shut-in time, and wait time for workover fluids, drive the need to control the rate of breaking the viscosity.
Background references include: U.S. Pat. No. 5,447,199 disclosing controlled degradation of polymer based aqueous gels; U.S. Pat. No. 6,924,254 disclosing viscous well treating fluids and methods using a delayed viscosity breaker comprising pentanedione peroxide; U.S. Pat. No. 6,489,282 disclosing bleaching compositions comprising a peroxy carboxylic acid and a polymer system; LUPEROX® Organic Peroxides Peroxyesters Product Bulletin (2005); and LUPEROX® Organic Peroxides General Catalog—Americas (2004).